Method of stabilizing olefinic gasoline by hydrofining with a chromium iron oxide catalyst



United States Patent METHOD OF STABILIZING OLEFINIC GASOLINE BYHYDROFINING WITH A CHROMIUM IRON OXIDE CATALYST Michael C. Chervenak,Trenton, Percival C. Keith, Peapack, and Helmut R. Pichler, Trenton,N.J., assignors to Hydrocarbon Research, Inc., New York, N.Y., aconporation of New Jersey No Drawing. Application August 26, 1954 SerialNo. 452,474

11 Claims. (Cl. 208-257) This invention relates to the treatment ofhydrocarbon oils and is more particularly concerned with the treatmentof raw cracked gasoline fractions. The invention is concerned primarilywith the treatment of raw cracked gasoline fractions to produce finishedgasoline of commercially acceptable storage stability and octane number.

This application is a continuation-impart of copending applicationSerial No. 416,446, filed March 15, 1954.

At the present time, motor gasoline is given ASTM D38l-50 test forexistent gum; in accordance with ASTM D439-52T gasoline specifications,the gasoline must show not more than 5 mg. of gum per 100 ml. Inaddition, petroleum refiners generally test gasoline for storagestability in accordance with ASTM D525-49 test. While no ASTMspecification has been adopted for the storage stability of gasoline,most refiners strive for an oxygen induction time of at least 300minutes as measured in ASTM D525-49 test. Finally, the demands of modernhigh compression engines make necessary the production of motor gasolinepossessing a high octane rating, usually determined as clear researchoctane number in accordance with ASTM D908-48T test.

In modern petroleum refining practice, it is highly advantageous toconvert part or all of the higher boiling fractions of the crude oil tomaterials boiling in the gasoline range. This is effected by processeswhich involve the cracking of the higher boiling hydrocarbons intohydrocarbons boiling in the gasoline range. However, in many cases, thegasoline fraction which is produced by cracking (hereinafter referred toas raw gasoline) requires further processing to provide a commerciallyaccepta'ble product having low gum content, good storage stability andhigh octane number. Various processes have been proposed for treatingsuch raw gasoline fractions to bring them within the desiredspecification limits, and some of these processes have been commerciallyused with varying effectiveness.

Cracked raw gasolines are generally of moderate to high octane number,containing to 50% by volume of aromatic hydrocarbons and at least 20% byvolume. of olefins. Known methods for removing gum-forming compoundsbring about the destruction or conversion of some of these unsaturatedhydrocarbons. For example, when hydrogenation at relatively highpressures and relatively low temperatures is employed, the olefinspresent in the cracked gasoline are hydrogenated to parafiins, thus:

It is well known that such paraflins have clear research octane numberswhich are as much as 40 octane numbers lower than the correspondingolefins from which they were formed. Thus, such treatment of a crackedraw gasoline fraction produces a finished gasoline which is generally ofappreciably lower clear research octane numher than the raw gasoline,and which is in all cases of lower clear research octane number thanwould have been obtained if said olefins had not been hydrogenated.

2,891,006 Patented June 16, 1959 Where the cracking operation produces araw gasoline which satisfies octane number requirements without theaddition of tetraethyl lead, e.g., above 83 clear research octanenumber, such utilization of conventional hydrogenation treatment toremove gum-forming compounds results in a finished gasoline which is ofconsiderably reduced clear octane number and which consequently requiressignificant quantities of anti-knock additives to achieve octanerequirements. Thus, the principal problem which these cracked rawgasoline fractions of high octane number and poor storage stabilitypresent is the reduction of gum-formers to commercially acceptablelimits without adverse. effect upon the clear research octane number.

A principal object of the present invention is to provide a process fortreating raw gasoline fractions containing at least 20% by volume ofolefins and an appreciable content of gum and/ or gum-forming compounds,which process will substantially eliminate said compounds, whilesubstantially preserving said olefins.

It is a further important object to provide a process for treating saidraw gasoline fractions, which will substantially eliminate saidgum-forming compounds, while increasing or at least maintainingunimpaired the octane ratings of said raw gasolines,

In accordance with the invention, a cracked raw gasoline fractioncontaining at least 20% by volume of olefins, and having anobjectionable content of gum and gumforming compounds, is introduced,together with hydrogen, into a treating zone maintained at a temperatureof 675 to 750 F., preferably at a temperature of about 700 to 725 F., incontact with particulate iron-chromium catalyst of the characterhereinbelow described. The total pressure in the treating zone and theintroduction of hydrogen and raw gasoline are controlled in known mannerto provide a hydrogen partial pressure of 50 to 250 p.s.i. (pounds persquare inch), preferably 50 to p.s.i. The total pressure of the systemmay vary over a relatively wide range, but it is generally preferred touse a total pressure not exceeding about 800 p.s.i.g. (pounds per squareinch gage).

The iron-chromium catalyst employed in the treating zone is derived froma mixture of iron. and chromium oxides in which mixture the chromiumoxide is the minor component. In most instances, the chromium oxide isin the range of 0.2 to 20% by weight of the catalytic oxide mixture, 0.5to 5% by weight of chromium oxide being frequently optimum. Suchcatalytic mixtures have been readily prepared by the co-precipitation ofthe iron and chromium oxides in the plus three valence states. hisnoteworthy that the catalyst of this process does not require a supportor carrier. In fact, iron-chromium oxide mixtures supported by carriershave been found less efiective than the unsupported oxides.

It is an outstanding advantage of this invention that the hydrogensupplied to the treating zone does not need to be in concentrated orpurified form. Rather, the economic attractiveness of the process stemsin large part from the fact that commonly available hydrogen-contain inggases having such components as the carbon oxides, methane and steam maybe utilized. In prior processes, such gaseous components have beenavoided. For instance, carbon monoxide is a poison to cobalt molybdatecatalysts and steam is deleterious to hydrogenation catalysts supportedon alumina and silica carriers.

The recently developed hydrocracking process disclosed,

for instance, in US. Patent 2,606,862 and copendingapgasoline is highlyolefinic and contains gum-forming bodies. 'The process of this inventionis particularly suited for the stabilization'of hydrocracked rawgasoline since the by-product gas of the hydrocracking operation willsatisfy the hydrogen requirements of the process without necessitatingany refinement of the gas or any supplementation of its hydrogen contentfrom an extraneoussource.

Another recent development which highlights the economic attractivenessof the present invention is the partial combustion of hydrocarbons withhigh-purity oxygen to produce a gas comprising hydrogen and carbonmonoxide as the predominant components. 'U.S. Patent 2,491,-

51 8 of E. W. 'Riblett discloses the production of such gas. Today,thepartial combustion of natural gas with oxygen obtained by theliquefaction and rectification of air o'ffersiin many localities thecheapest source of hydrogen. Consequently, olefinic raw gasolines cannow be stabilized against gum formation very economically by thisinvention utilizing as the hydrogen-containing gas the product of thepartial combustion process without any intermediate treatment.

Interestingly enough, when the hydrogen-containing gas fed to thetreating zone also contains carbon monoxide and Water vapor inappreciable quantities, the tail gas of this process may be richer inhydrogen than the gas supplied'th'ereto even though hydrogen is consumedor taken up by the gum-forming bodies of the raw gasoline undergoingtreatment. This is possible in the present process because theiron-chromium oxide catalyst is capable of promoting simultaneouslystabilization and the water-gas shift reaction:

There is reason to believe that treating raw gasoline pursuant to thisinvention with gas that undergoes the water-gas shift reaction isparticularly desirable because nascent hydrogen will more readily attackthe gum-forming compounds.

The hydrogen-containing gas will preferably comprise at least about 20%by volume of hydrogen in order to avoid the necessity of passingexcessively large amounts ofgas through-the reaction zone to provide thedesired hydrogen partial pressure of 50 to 250 'p.s.i. and in order toavoid the necessity of raising the total pressure of the system to ahigh value. The amount of hydrogen supplied to the treating or reactionzone generally falls in the range of 300 to 3000 standard cubic feet perbarrel of raw gasoline, preferably in the range of 1000 to 2000 standardcubic feet per barrel.

Treatment of the cracked raw gasoline in the reaction zone under thespecified conditions is carried out to an extent sufficient to improveits stability to the desired degree. Advantageously, the desiredreaction is insured by employing a raw gasoline feed "rate in the rangeof 1 to 5-, preferably 2 to 3, volumes of liquid per hour per volume ofcatalyst.

The term gasoline fraction as "herein used has its conventional meaning,viz., a hydrocarbon fraction boiling within the temperature range of 90to 400 F., although it will be apparent that the treating process ofthis invention is applicable to hydrocarbon fractions in which materialboiling within the gasoline range comprises the predominant portion ofthe fraction.

Cracked raw gasoline fractions from various sources are advantageouslytreated in accordance with the process of the invention'but'the-improvedprocess is of particular value, .as already mentioned,in eliminating the gum-formers of hydrocracked ra-w gasoline fractionsof relatively high octane'number, e.g., clear research octane numbersofabout 80 to 90, containing substantial quantities 'of mono-olefins.Frequently, the olefins amount to at least 30% by volume of the rawgasoline. As previously pointed'out, the" present process is effectiveto remove even large proportions of gum forming bodies,

4 without any appreciable change of the high octane number of the rawgasoline. In some cases the octane number is raised one or two units.

Without tying the invention to any particular theory of operation, theprocess appears to involve the conversion of gum-forming diolefins tostable mono-olefins. At the same time, aromatic hydrocarbons andmonoolefins are substantially not affected so that the excellentanti-knock properties of the raw gasoline are not impaired.

Under the conditions of this process, there is such limitedpolymerization or other degradation of the gasoline hydrocarbons thatthe deposition of carbonaceous matter on the catalyst may be held toless than about 0.1% by weight of the raw gasoline and often to lessthan about 0.01%. Thus, the catalyst may be used for long periodswithout regeneration to efiect removal of the carbonaceous deposit. Forinstance, operating the process with a fixed bed of iron-chromium oxidecatalyst and a raw gasoline feed rate of 2 liquid volumes per hour pervolume of catalyst, the on-stream time will be over 150 hours and may beseveral times as much. At the same time, no high-boiling hydrocarbonsare formed so that the treated gasoline does not require fractionationto separate out any polymers or heavy hydrocarbons. The reated gasolinewill generally amount to at least about 99% by volume of the rawgasoline and may even exceed 100%. Not more than about 0.5% by Weight ofthe raw gasoline is converted to normally gaseous hydrocarbons (C -C Thefinished gasoline fraction recovered from the reaction efliuent is ofhigh stability and high octane number and meets the specifications forcommercial motor gasoline notwithstanding the presence of a substantialquantity of diolefins originally in the cracked raw gasoline.

The particular apparatus used for the process and the particular methodof regenerating the catalyst form no part of the present invention andany convenient apparams and method of catalyst regeneration may beemployed. In regenerating the catalyst care must be taken, however, inaccordance with commercial regeneration techniques, to avoid the use oftemperatures which destroy or adversely affect the catalyst. In theregeneration of the catalyst of the present process, temperatures inexcess of 1100 F. are generally to be avoided.

In order to facilitate the maintenance of the desired temperature in thereaction zone, the cracked raw gasoline to be treated is advantageouslypreheated to a temperature of 400 to 750 F., preferably about 500 to 700F, before being fed into the reaction zone. The hydrogen-containing gasmay also be preheated to about the same temperature as the raw gasoline.

For a further understanding of the invention, reference is made to thefollowing specific examples which are intended as illustrative and notlimitative of the process.

Example 1 A raw gasoline obtained by high-severity catalytic cracking ofa heavy'oil contains 0.19% by weight of sulfur largely in the form ofrefractory compounds and over 40% by volume of olefins.

This raw gasoline and hydrogen-containing gas are brought into contactwith a catalyst composed 'of 92% by weight of iron oxide and 8% byweight of chromium oxide, the mixed oxides having been co-precipitated.The gas has an approximate composition on a volume basis of 37% H 19% COand 44% H O. This gas is charged to the reaction zone at a ratecorresponding to 1500 standard cubic feet of hydrogen per barrel of rawgasoline charged therewith to maintain ahydrogen partial pressure ofabout 100 psi. in the reaction zone. The space velocity of the rawgasoline is 2.0 liquid volumes per hour per volume of catalyst. Thereaction zone is maintained at a temperature of 715 F. The finishedgasoline recovered from the reaction eflluent amounts to 99.9% by volumeof the raw gasoline.

The improvement of the gasoline achieved by the process is evident froma comparison of its properties, before and after treatment:

Raw Finished Gasoline Gasoline Example 2 The hydrooracking ofMid-Continent 10% residuum yields a raw gasoline containing over 50% byvolume of olefins.

This highly olefinic gasoline is treated with the hydrogen-containinggas and iron-chromium oxide catalyst of Example 1 at a temperature of715 F. The reaction conditions include a hydrogen partial pressure of100 p.s.i., a hydrogen flow rate of 2600 standard cubic feet per barrelof gasoline and a raw gasoline space velocity of 2.0 liquid volumes perhour per volume of catalyst. The yield of finished gasoline correspondsto 100.5% by volume of the raw gasoline.

The properties of the gasoline, before and after treatment, are asfollows:

Raw Finished Gasoline Gasoline While the catalyst used in the process ofthis invention is customarily supplied to the reactor in the form ofmixed iron and chromium oxides, it is well to note that during operationthe oxide mixture undergoes some change so that the catalyst comprisesiron and chromium as a mixture of the oxides, sulfides and elementalmetals. In fact, it is sometimes advisable to pretreat the freshlyprepared oxide mixture with hydrogen to eifect partial reduction andthus supply the catalyst to the reaction in a state more nearly likethat attained during operation of the process when the catalyst reachesa high level of activity.

It is to be observed that under the process conditions of thisinvention, refractory sulfur compounds such as thiophenes and likecyclic sulfur compounds remain unaltered. However, these processconditions will generally eliminate a material proportion of mercaptansthat may be present in the raw gasoline. Accordingly, the process ofthis invention is for the degumming and stabilizing treatment ofsubstantially sweet cracked raw gasolines, i.e., gasolines containingnot more than about 0.3% by weight of sulfur in the form of refractorycompounds. Where the raw gasoline requires elimination of a materialquantity of refractory sulfur compounds contained therein, the processconditions of the aforementioned application Serial No. 416,446 shouldbe employed.

The recently developed hydrocracking process for producing gasoline fromheavy oils yields raw gasoline fractions having the followingapproximate composition by volume):

0-20% paraffins and naphthenes 2540% aromatics 30-60% olefins 2-10%diolefins The diolefins, acyclic and cyclic, which are known to bemainly responsible for high gum content and/or poor storage stability ofgasoline (Sachanen, Conversion of Petroleum, 2nd edition, 1948,Rheinhold Publishing Corp., page 498), are substantially converted todesirable mono-olefins by the process of this invention. In this Way,the hydrocracked raw gasoline is degummed and stabilized withoutimpairment of the excellent anti-knock properties of the raw gasolineand simultaneously a high yield of finished gasoline that is often onthe order of 100.5% by volume of the raw gasoline is obtained.

In view of the various modifications of the invention which will occurto those skilled in the art upon consid eration of the foregoingdisclosure without departing from the spirit or scope thereof, only suchlimitations should be imposed as are indicated by the appended claims.

What is claimed is:

1. A vapor-phase process for eliminating gum-forming constituents from ahighly olefinic hydrocarbon fraction, which comprises bringing hydrogenand a vaporized hydrocarbon fraction containing gum-forming constituentsand more than 20% by volume of olefins imparting to said hydrocarbonfraction a high octane number into contact with an iron-chromium oxidecatalyst containing chromium oxide in the range of 0.2 to 20% by weightof the catalytic oxide mixture in a reaction zone maintained at atemperature in the range of 675 to 750 F., efiecting reaction betweensaid hydrogen and said vaporized hydrocarbon fraction during contactwith said catalyst to the extent that there is a net consumption ofhydrogen without hydrogenation of at least a major portion of saidolefins, passing said hydrocarbon fraction through said reaction zone ata space velocity in the range of about 1 to 5 liquid volumes per hourper volume of said catalyst, maintaining the partial pressure ofhydrogen in said reaction zone in the range of 50 to 250 p.s.i., andrecovering from the resulting vaporized reaction effluent a highlyolefinic hydrocarbon fraction with a substantially decreased content ofgum-forming constituents and containing at least a major portion of saidolefins and having a high octane number.

2. A vapor-phase process for eliminating gum-forming constituents from ahighly olefinic hydrocarbon fraction, which comprises bringing hydrogenand a vaporized hydrocarbon fraction containing gum-forming constituentsand more than 30% by volume of olefins imparting to said hydrocarbonfraction a high octane numher into contact with an iron-chromium oxidecatalyst containing chromium oxide in the range of 0.2 to 20% by weightof the catalytic oxide mixture in a reaction zone maintained at atemperature in the range of 700 to 725 F., effecting reaction betweensaid hydrogen and said vaporized hydrocarbon fraction during contactwith said catalyst to the extent that there is a net consumption ofhydrogen Without hydrogenation of at least a major portion of saidolefins, passing said hydrocarbon fraction through said reaction zone ata space velocity in the range of about 1 to 5 liquid volumes per hourper volume of said catalyst, maintaining the partial pressure ofhydrogen in said reaction zone in the range of 50 to a 250 p.s.i., andrecovering from the resulting vaporized reaction effluent a highlyolefinic hydrocarbon fraction with a substantially decreased content ofgumform constituents and containing at least a major portion of saidolefins and having a high octane number.

3. A vapor-phase process for eliminating gum-forming constituents from ahighly olefinic gasoline fraction, which comprises bringing hydrogen anda vaporized gasoline fraction containing more than 2% by volume ofdiolefins and more than 30% by volume of olefins and having a clearresearch octane number of at least about into contact with aniron-chromium oxide catalyst containing chromium oxide in the range of0.2 to 20% by weight of the catalytic oxide mixture in a reaction zonemaintained at a temperature in the range of 675 to 750 F., effectingreaction between said hydrogen and said vaporized gasoline fractionduring contact with said catalyst to the extent that there is a netconsumption 'of hydrogen without hydrogenation of at least a majorportion of said olefins, passing said gasoline fraction through saidreaction zone at a space velocity in the range of about 1 to liquidvolumes per hour per volume of said catalyst, maintaining the partialpressure of hydrogen in said reaction zone in the range of 50 to 250p.s.i., and recovering from the resulting vaporized reac- I tion.eflluent a high olefinic gasoline fraction with a'substantiallydecreased content of said diolefins and containing at least a majorportion of said olefins and having a clear research octane number of atleast about 80.

4. A vapor-phase process according to claim 3 wherein the iron-chromiumoxide catalyst is derived by the coprecipitation of the iron andchromium oxides, and the hydrogen partial pressure is in the range of 50to 150 psi.

5. A vapor-phase process according to claim 3 wherein the hydrogensupplied to the reaction zone is admixed with a substantial quantity ofa gas selected from the group consisting of carbon monoxide, carbondioxide, water vaporandmixtures thereof.

6. A vapor-phase process for refining a highly olefinic gasoline, whichcomprises bringing hydrogen and a vaporized raw gasoline containing atroublesome quantity of gum-forming bodies and containing more than 20%by volume of olefins, said raw gasoline having a clear reasearch octanenumber of at least about 80, into contact with an iron-chromium oxidecatalyst containing chromium oxide in the range of 0.2 to 20% by weightof the catalytic oxide mixture in a reaction zone maint ain ed at atemperature in the range of 700 to 725 F, eflFecting reaction betweensaid hydrogen and said vaporized raw gasoline during contact with saidcatalyst to the extent that there is a net consumption of hydrogenwithout hydrogenation of at least a major portion of said olefins,passing said raw gasoline through said reaction zone at a space velocityin the range of about 1 to 5 liquid volumes per hour per volume of saidcatalyst, maintaining the partial pressure of hydrogen in said reactionzone in the range of 50 to 150 p.s.i., and recovering from the resultingvaporized reaction effluent a highly ole'finic finished gasolinesubstantially free of said gum-forming bodies and containing at least20% by volume of said olefins and having a clear research octane numberover 80.

7. A vapor-phase process according to claim 6 wherein the iron-chromiumoxide catalyst is derived by the coprecipitation of the iron andchromium oxides, the chromium oxide being inthe range of 0.5 to 5% byweight of the co -precipitated oxides. g

8. A vapor-phase process according to claim 6 where in the raw gasolinepasses through the reaction zone at a space velocity in the range ofabout 2 to 3 liquid volumes per hour per volume of catalyst.

9. A vapor-phase process according to claim 8 wherein the raw gasolinecontains more than 30% by volume of olefins and the hydrogen supplied tothe reaction zoneis admixed With substantial quantities of carbonmonoxide and water vapor.

10. A vapor-phase process for refining a highly olefinic gasoline, whichcomprises bringing hydrogen and a vaporized raw gasoline containing atroublesome quantity of gum-forming bodies and containing more than 20%by volume of olefins imparting to said raw gasoline a high octane numberinto contact with an iron-chromium oxide catalyst containing chromiumoxide in the range of 0.2 to 20% by weight of the catalytic oxidemixture in a reaction zone maintained at a temperature in the range of675 to 0 F, elfecting reaction between said hydrogen and said vaporizedraw gasoline during contact with said catalyst to the extent that thereis a net consumption of hydrogen without hydrogenation of at least amajor. portion ofsaid olefins, passing said raw gasoline through saidreaction zone at a space velocity in the range of about 1 to 5 liquidvolumes per hour per volume of said catalyst, maintaining the partialpressure of hydrogen in said reaction zone in the range of 50 to 250p.s.i., and recovering from the resulting vaporized reaction effluent ahighly olefinic finished gasoline substantially free of said gum-formingbodies and containing at least 20% by volume of said olefins and havinga high octane number and an oxygen induction time of at least 300minutes.

11. A vapor-phase process according to claim 10 wherein the raw gasolinepasses through the reaction zone at a space velocity in the range ofabout 2 to 3 liquid volumes per hour per volume of catalyst.

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1. A VAPOR-PHASE PROCESS FOR ELIMINATING GUM-FORMING CONSTITUENTS FROM AHIGHLY OLEFINIC HYDROCARBON FRACTION, WHICH COMPRISES BRINGING HYDROGENAND VAPORIZED HYDROCARBON FRACTION CONTAINING GUM-FORMING CONSTITUENTSAND MORE THAN 20% BY VOLUME OF OLEFINS IMPARTING TO SAID HYDROCARBONFRACTION A HIGH OCTANE NUMBER INTO CONTACT WITH AN IRON-CHROMIUM OXIDECATALYST CONTAINING CHROMIUM OXIDE IN THE RANGE OF 0.2 TO 20% BY WEIGHTOF THE CATALYTIC OXIDE MIXTURE IN A REACTION ZONE MAINTAINED AT ATEMPERATURE IN THE RANGE OF 675 TO 750* F., EFFECTING REACTION BETWEENSAID HYDROGEN AND SAID VAPORIZED HYDROCARBON FRACTION DURING CONTACTWITH SAID CATALYST TO THE EXTENT THAT THERE IN A NET COMSUMPTION OFHYDROGEN WITHOUT HYDROGENATION OF AT LEAST A MAJOR PORTION OF SAIDOLEFINS, PASSING SAID HYDROCARBON FRACTION THROUGHT SAID REACTION ZONEAT A SPACE VELOCITY IN THE RANGE OF ABOUT 1 TO 5 LIQUID VOLUMES PER HOURPER VOLUME OF SAID CATALYST, MAINTAINING THE PARTIAL PRESSURE OFHYDROGEN IN SAID REACTION ZONE IN THE RANGE OF 50 TO 250 P.S I., ANDRECOVERING FROM THE RESULTING VAPORIZED REACTION EFFLUENT A HIGHLYOLEFINIC HYDROCARBON FRACTION WITH A SUBSTANTIALLY DECREASED CONTENT OFGUM-FORMING CONSTITUENTS AND CONTAINING AT LEAST A MAJOR PORTION OF SAIDOLEFINS AND HAVING A HIGH OCTANE NUMBER.